You can use wikis for any kind of collaborative assignments that you might assign that could be done in a virtual space. (Alas, building a house is not one of those things, but making plans for building a house could be.)
Those might include, but are not limited to:
Writing a paper, script, or other written product
Creating a podcast
Creating a PhotoStory
Creating a PowerPoint
Creating a video
Planning for any kind of project
Having an online discussion (which will often encourage students who are less willing to contribute "in real life" to add their "voice" to the discussion)
Sharing resources of any variety (videos, links, articles)
Writing workshop
Blogging
Collecting & organizing resources for your classes
Calendar of homework
Videos
Audio files (podcasts, music, etc.)
Assignments
Polls
Quizzes
Links
Some amazing resources for using wikis in your classes:
Those might include, but are not limited to:
Some amazing resources for using wikis in your classes:
Educational Wikis wiki
Troy Hicks - Digital Writing Workshop wiki
Blogs, Wikis, Podcasts, and Other Powerful Web Tools for Classrooms (pdf book)